“It is my view that the whole report should be published immediately,” the letter stated.

“The public interest demands it. There are no countervailing considerations such as national security or the administration of justice.

“The national implications of the report’s subject matter are also a reason for the report to be made available for consideration and criticism without delay.”

Mr Walker’s letter also urged the Government to keep the commission’s own website online for longer, so readers could check his findings against lengthy and complex documents and transcripts given in evidence.

“This is all the more important because my conclusions include adverse assessments of many governmental decisions and processes,” the letter said.

“The criticism and justification of governmental conduct is peculiarly, in our society, best done openly.”

Fish kills will not be investigated

In the letter, Mr Walker volunteered himself to investigate recent fish kills in the lower Darling and various political, official and community responses to them.

“If the Government were interested to investigate these matters in relation to the proper concerns of South Australia in them, I would be willing to accept an appropriately tight, limited and economic extension of the time for a final report, so as to encompass these recent events in my work,” the letter said.

But Ms Chapman today declined the offer of an extension.

“I note that the cost to date of the commission is $5.017 million,” she wrote.

“Extending the royal commission would be an unfair burden on South Australian taxpayers given the sum already spent.”

Crossbench senators have used the latest disagreement to accuse the South Australian Liberal Government of running a “protection racket” for Liberal governments elsewhere in the country.

South Australian Greens senator Sarah Hanson-Young said the suggestion the report may not be released immediately showed a contempt for the public.

“The South Australian Government should not be running a protection racket for their federal counterparts and release this report immediately when the commissioner delivers it,” she said.

“It’s political interference like this that warrants a federal royal commission as a matter of urgency.”

Centre Alliance senator Stirling Griff questioned whether the SA Government may be seeking to delay the release of the report beyond the NSW election on March.

“This is not a political issue. It should not be a political issue,” he said.

“If they are trying to delay it beyond the New South Wales election, I think everyone will see through that.”

State Opposition Leader Peter Malinauskas said whether the Premier delayed the release of the report or not would be “a key test of whether Steven Marshall is standing up for South Australia and the Murray or taking his orders from the eastern states”.